979
FXUS02 KWBC 251845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST MON NOV 25 2024
VALID 12Z THU NOV 28 2024 - 12Z MON DEC 02 2024
...UNSETTLED WEATHER FOR THANKSGIVING TO BE FOLLOWED BY FIRST
SIGNIFICANT ARCTIC AIR BLAST AND LAKE EFFECT SNOW EVENT...
..OVERVIEW
FOR THANKSGIVING DAY INTO THE WEEKEND, THE LARGE SCALE WEATHER
PATTERN WILL UNDERGO A CONSIDERABLE TRANSITION, WITH A NORTHERN AND
SOUTHERN STREAM SHORTWAVE ENERGY COMBINING INTO A BROAD, LARGE
SCALE TROUGH OVER MUCH OF THE CENTRAL TO EASTERN UNITED STATES. THE
LOW PRESSURE SYSTEM TRACK AND SENSIBLE WEATHER ON THE LEADING EDGE
OF THIS PATTERN CHANGE REMAINS UNCERTAIN THOUGH GUIDANCE HAS
TRENDED CLOSER TOWARD A COMMON SCENARIO TODAY. A WET, UNSETTLED
THANKSGIVING IS LIKELY FOR MANY ACROSS THE EAST WITH A THREAT OF
WINTRY PRECIPITATION AND HEAVY SNOW FOR THE INTERIOR NORTHEAST.
HOWEVER, IN THE WAKE OF THIS PASSING SYSTEM, THE WEATHER WILL TURN
SHARPLY COLDER WITH AN INTRUSION OF ARCTIC AIR FROM THE NORTHERN
ROCKIES AND NORTHERN PLAINS THROUGH THE EASTERN SEABOARD. THIS WILL
USHER SOME OF THE COLDEST AIR OF THE SEASON SO FAR AND WILL BRING
A FAVORABLE SETUP FOR SIGNIFICANT LAKE EFFECT SNOW DOWNWIND OF THE
GREAT LAKES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE GREATEST MODEL UNCERTAINLY AND IMPACTS TO SENSIBLE WEATHER LIE
WITH THE BEGINNING OF THE FORECAST PERIOD - THANKSGIVING DAY - WITH
THE LARGE SCALE PATTERN UNDERGOING A SIGNIFICANT CHANGE. WHILE ALL
OF THE AVAILABLE GUIDANCE DOES SHOW SHORTWAVE ENERGY WITHIN THE
DEVELOPING TROUGH OVER THE CENTRAL AND EAST, THE POSITION/STRENGTH
OF THE FEATURE REMAINS SOMEWHAT UNCERTAIN. WHILE OVER THE PAST FEW
DAYS THERE WERE LARGE TIMING AND SPATIAL DIFFERENCES, AT LEAST
TODAY THE SPATIAL SPREAD HAS LESSENED AND SEEMS TO BE CONVERGING
ON A COMMON SCENARIO. THE LATEST GFS HAS TRENDED CLOSER TO THE
ECMWF/CMC SOLUTION, BRINGING THE LOW PRESSURE SYSTEM ACROSS THE
OHIO VALLEY INTO THE MID-ATLANTIC (COMPARED TO A SOUTHERN SOLUTION
ADVERTISED OVER THE PAST FEW DAYS). IT'S STILL ON THE SOUTHERN SIDE
OF THE MODEL SPREAD, WHILE THE LATEST ECMWF REMAINS
SHARPER/STRONGER WITH THE SHORTWAVE ENERGY AND THEREFORE WRAPS
PRECIPITATION FURTHER NORTH/INTERIOR INTO THE NORTHEAST. SO WHILE
THERE IS GREATER CONFIDENCE ON A WET/RAINY PERIOD FOR THE MID-
ATLANTIC, THE NORTHERN EXTENT (AND POSSIBLE SNOW ACCUMULATIONS)
REMAINS A BIT LESS UNCERTAIN BUT BEARS WATCHING FOR POTENTIALLY
IMPACTFUL HOLIDAY WINTER WEATHER FOR SOME INTERIOR NORTHEAST
LOCATIONS. IF THE ECMWF- LIKE SCENARIO WERE TO VERIFY, A WET/HEAVY
SNOW WOULD OCCUR WITH SOME POTENTIAL FOR SIGNIFICANT ACCUMULATIONS.
THE WPC FORECAST TRIED TO STRIKE A BALANCE BETWEEN THE MOST
SUPPRESSED AND THE FARTHEST NORTHERN SOLUTIONS WITH A BLEND OF THE
DETERMINISTIC GUIDANCE EARLY ON RESULTED IN A FAVORABLE SOLUTION
AND TRENDED WELL WITH CONTINUITY.
BEYOND THURSDAY, THE WEATHER PATTERN BECOMES A BIT MORE PREDICTABLE
WITH THE BROAD TROUGHING ENCOMPASSING MUCH OF THE CENTRAL AND
EASTERN UNITED STATES. A QUICK MOVING SHORTWAVE TROUGH IS LIKELY TO
PASS THROUGH THE PLAINS, MIDWEST, AND OHIO VALLEY FRIDAY/SATURDAY,
POTENTIALLY BRINGING A STREAK OF LIGHT PRECIPITATION. TEMPERATURE
PROFILES WOULD SUPPORT MOSTLY LIGHT SNOW, SO A POSSIBLE AREA TO
WATCH FOR IMPACTFUL SNOW ACCUMULATIONS INTO THE WEEKEND FOR SOME
AREAS. THE VARIOUS MODELS DO DISAGREE ON THE TIMING/POSITION OF
THIS FEATURE, WHICH APPEARS TO BE WITHIN THE NORMAL SPREAD FOR THIS
FAR OUT ON A SUBTLE SHORTWAVE.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC MODELS
FOR DAYS 3-5 FOLLOWED BY A 50 PERCENT BLEND OF THE ECENS AND GEFS
MEANS. OVERALL, THE NBM QPF LOOKED REASONABLE FOR THURSDAY THEN
WITH THE SIGNIFICANT LAKE EFFECT SNOW POTENTIAL, QPF WAS NUDGED
HIGHER IN THE FAVORED LOCATIONS USING SOME OF THE DETERMINISTIC
GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
FOR THANKSGIVING DAY, THE EAST COAST WEATHER SYSTEM WILL BRING
WIDESPREAD PRECIPITATION FROM THE SOUTHEAST INTO THE NORTHEAST.
SOME OF THE RAIN COULD BE MODERATE IN INTENSITY AROUND THE
CAROLINAS BUT LIKELY FALLS SHORT OF INTRODUCING AN EXCESSIVE
RAINFALL OUTLOOK AT THIS TIME. FOR THE MID-ATLANTIC AND THE
NORTHEAST, A MOSTLY COLD RAIN IS EXPECTED THROUGH FOR FAR INTERIOR
LOCATIONS, A MIX OF RAIN/SNOW IS LIKELY, WITH THE GREATEST
POTENTIAL FOR HEAVY/WET SNOW FOR THE HIGHER ELEVATIONS OF THE
ADIRONDACKS, GREENS, WHITES, AND INTERIOR MAINE. THERE REMAINS SOME
UNCERTAINTY ON THE STRENGTH AND INTENSITY OF LOW PRESSURE AND SOME
OF THIS WINTER PRECIPITATION COULD BE HEAVY FOR THE INTERIOR
NORTHEAST LOCATIONS, BRINGING SOME LOCATIONS A WHITE THANKSGIVING.
THE DAY 4 WINTER WEATHER OUTLOOK IS CURRENTLY ADVERTISING MODERATE
CHANCES (50 TO 70 PERCENT) FOR IMPACTFUL SNOW (LIQUID EQUIVALENT
OF AT LEAST 0.25") AND THIS SYSTEM BEARS WATCHING FOR POTENTIALLY
SIGNIFICANT/IMPACTFUL HOLIDAY WINTER WEATHER.
IN THE WAKE OF THIS SYSTEM, A VERY PRONOUNCED UPPER LEVEL TROUGH
WILL SETTLE OVER THE CENTRAL AND EASTERN UNITED STATES. A
SIGNIFICANT ARCTIC AIR INTRUSION WILL BRING SOME OF THE COLDEST AIR
OF THE SEASON SO FAR TO PLACES FROM THE NORTHERN PLAINS AND
NORTHERN ROCKIES EASTWARD. THE COLD AIR WILL ARRIVE FIRST ON
THANKSGIVING DAY AND FRIDAY AND SPREAD EASTWARD THROUGH THE
WEEKEND. THE COMBINATION OF THE VERY COLD TEMPERATURES AND WINDY
CONDITIONS WILL BRING DANGEROUSLY COLD WIND CHILLS TO PARTS OF THE
NORTHERN PLAINS AND UPPER MIDWEST. HIGH TEMPERATURES WILL BE IN THE
SINGLE DIGITS TO TEENS AND OVERNIGHT LOWS WELL BELOW ZERO. WIND
CHILL READINGS ACROSS MUCH OF NORTH DAKOTA WILL BE BELOW NEGATIVE
20F. THIS WILL POSE AN INCREASED RISK OF HYPOTHERMIA AND FROSTBITE
ON EXPOSED SKIN.
HEAVY LAKE-EFFECT SNOW IS EXPECTED FRIDAY THROUGH SUNDAY,
DEVELOPING EAST/SOUTHEAST OF THE LAKES AND RESULTING IN SIGNIFICANT
ACCUMULATIONS FOR SOME OF THE FAVORED LAKE EFFECT LOCATIONS. TRAVEL
DISRUPTIONS ARE LIKELY ESPECIALLY ON I-90 BETWEEN CLEVELAND AND
BUFFALO AND I-81 NORTH OF SYRACUSE. WHILE FORECAST ACCUMULATIONS
WILL BECOME CLEARER OVER THE NEXT FEW DAYS, THE LATEST WINTER
WEATHER OUTLOOK IS HIGH (ABOVE 70 PERCENT) IN THE FAVORED SPOTS,
ESPECIALLY DOWNWIND OF LAKE ERIE AND LAKE ONTARIO.
ELSEWHERE, A QUIETER PERIOD IS LIKELY FOR THE WEST PRECIPITATION-
WISE. PARTS OF CALIFORNIA MAY SEE LIGHT TO LOCALLY MODEST
PRECIPITATION AT TIMES LATER THIS WEEK INTO THE WEEKEND WITH SOME
ENERGY ALOFT, WITH SOME LIGHT AMOUNTS PERHAPS SPILLING INTO THE
SOUTHWEST. THE SAME GOES FOR THE PACIFIC NORTHWEST INTO THE
NORTHERN ROCKIES. MODELS ARE STARTING TO SHOW A GENERAL SIGNAL FOR
A ROUND OF LIGHT TO MODERATE SNOW ACROSS PARTS OF THE NORTHERN
PLAINS ON FRIDAY INTO THE MID-MISSISSIPPI AND OHIO VALLEYS
SATURDAY. OVER THE WEEKEND AND EARLY NEXT WEEK, RETURN FLOW OF
MOISTURE COULD START TO COME INTO THE WESTERN GULF COAST REGION FOR
SOME SHOWER ACTIVITY.
TATE/TAYLOR
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC MEDIUM
RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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